This invention relates generally to pneumatic braking systems and, more particularly to a latching exhaust valve (LEV) for a pneumatic braking system.
For over one hundred years, train braking has been accomplished pneumatically. Pure air braking operates in the following manner. Air brakes on each rail car in a train respond to air signals from a brake pipe running the length of the train. When an engineer operates a locomotive brake valve to stop or slow the train, air pressure is reduced along the brake pipe, causing a brake control valve in each rail car to release air from a reservoir to apply the car brake. When brake pipe air pressure is increased, the brake control valve causes the brake to be released and allows the air supply reservoir to be recharged with air.
Because time is required for brake pipe air to travel from one car to the next, pure air braking is slow and uneven over the length of the train. For example, it can take as long as 15 seconds for a brake pipe pressure change to travel the length of a train having 150 rail cars. For this reason, electronically controlled braking systems have been developed to provide for substantially uniform and simultaneous braking on all cars. However, often times exhaust valves utilized with electronically controlled braking systems operate pneumatically. In addition, sometimes braking is applied for extended periods of time, e.g., longer than one hour.